1. Field of the Invention
The present invention relates to a radio frequency (RF) input device of a superspeed optical communications module which controls the performance of a module in the superspeed (2.5 Gbps, 10 Gbps) optical communications module.
2. Description of the Related Art
A 2.5/10 Gbps module, an essential component of superspeed optical communications, has drastically improved performance by changing the shape of a microstrip line used in the prior art, in order to improve characteristics such as 3 dB bandwidth and RF return loss, which are essential parameters of the module.
FIG. 1A is a plan configuration view of an RF input device of a conventional superspeed optical communications module. FIG. 1B is an equivalent circuit diagram of the RF input device of FIG. 1A. As shown in FIGS. 1A and 1B, an RF input device of a superspeed optical communications module includes a microstrip line pattern 5 of a constant width formed on a microwave substrate 6. An electroabsorption modulated laser (EML) chip 9 comprised of a laser diode 9a and a modulator 9b is mounted on a thin film resistor 8 and an EML submount 10. The microstrip line pattern 5 is connected to the thin film resistor 8 and the EML chip 9 by bonding wires 7. Here, the bonding wire is usually an Au wire having a thickness of 1 mm, and the length thereof is as short as possible to minimize a generated inductance component. A thin film or chip resistor 8 having a resistance of 45 to 55.OMEGA. is connected to the EML chip 9 to achieve impedance matching with the EML chip 9.
Reference numeral 1 in FIG. 1B denotes an inductance component due to a bonding wire used within a module, reference numeral 2 denotes a 2.5 Gbps or 10 Gbps EML, and reference numeral 3 denotes a thin film resistor or chip resistor having a resistance of 45 to 55.OMEGA. used to achieve impedance matching of a high speed module.
The microstrip line 5 is a metallic line formed so that the characteristic impedance simply matches with a resistance of 50.OMEGA.. The thus-formed microstrip line 5 cannot solve degradation of module characteristics caused by the bonding wire 7 and a capacitance component formed in the EML chip 9 and other parts, and has an 8 GHz 3 dB bandwidth (.vertline.S21.vertline.) and an RF return loss (.vertline.S11.vertline.) of about 11 dB as shown in FIG. 2, so that it becomes a problem in high-speed transmission. That is, the microstrip line 5 does not meet a current specification of 15 dB or more, so that there is a problem in its operation at 10 Gbps. Also, a great deal of heat is generated due to simultaneous consumption of direct current and alternating current power in a resistance of 45 to 55.OMEGA..